MKI67 and pelvic inflammatory disease: We confirmed proliferation of newly formed PIDs by immunostaining with Ki-67, a proliferation marker, to determine whether these cells exhibited proliferative activity similar to ES cells; however, Ki-67-expressing cells were not detected in PIDs from SSEA-4+ cells (Fig. 6i) or in PIDs from CA19-9+ cells (Fig. 6j), and few Ki-67 cells were detected in adult PID tissues (Additional file 2: Figure S1g).